1. Technical Field of the Invention
The present invention relates to a shroud structure which shrouds a turbine rotator blade of a gas turbine.
2. Description of the Related Art
In a gas turbine, an air compressor compresses air, a combustor combusts fuel in the compressed air, combustion gas drives the turbine, and the air compressor is driven by the driving force.
When an operation temperature of the gas turbine is raised, efficiency is improved. Therefore, the turbine rotator blade, and a turbine shroud and turbine casing which shroud the blade is cooled, and the gas turbine is operated at a high temperature, so that the efficiency has heretofore been improved.
In recent years, from a necessity of enhancement of capability required for development of a jet-engine and consideration to environment, and it has been an important problem to reduce a cooling air amount as well as an engine weight.
A heat-resistant metal has heretofore been used in the turbine shroud, but in recent years a material particularly superior in a high-temperature characteristic has been applied with the high temperature of a turbine portion. Moreover, a thermal barrier coating which is a thermal interference layer is sometimes applied. However, for the metal turbine shroud, it has already been impossible to further reduce the cooling air or weight. For the present situation in which the temperature tends to be further raised, the amount of the cooling air has to be increased. Moreover, the weight cannot be reduced. In other words, metal components have already reached their limitations, and further reduction of the cooling air amount or weight cannot be expected in the situation.
To solve these problems, a shroud of a ceramic composite material (CMC) has also been proposed (e.g., Japanese Patent Application Laid-Open Nos. 10-103013, 10-103014).
In “Gas Turbine Shroud Structure” of the Japanese Patent Application Laid-Open No. 10-103013, as shown in FIG. 1, a cylindrical shroud 1 is constituted of a plurality of segments 2 which are divided a peripheral direction to have circular-arc plate shapes. Opposite edges of each segment along a main-stream gas direction are supported by a support member 4 fixed on an inner peripheral side of a gas turbine casing 3, and each segment 2 is constituted of ceramic and has a double plate structure which includes an outer peripheral side plate portion 2a and inner peripheral side plate portion 2b. It is to be noted that in this diagram, reference numeral 5 denotes a first-stage stationary blade, and 6 denotes a first-stage rotator blade.
However, in the shroud in which such two-dimensional plate-shaped CMC material is used, delamination occurs, a high stress is generated in a portion formed by combining two components 2a, 2b by deformation at a high temperature, and there is a problem of high possibility that the portion is destroyed.
On the other hand, in “Gas Turbine shroud Structure” (FIG. 2) of the Japanese Patent Application Laid-Open No. 10-103014, the respective segments 2 in FIG. 1 are constituted of ceramic, and a section of the segment has a hollow constitution which has a square, trapezoidal, I or another shape by braiding.
However, in the shroud using the braided CMC material, many fibers cannot be included in the braided material. When the segment is lengthened, thermal stress increases. There is a problem that it is difficult to establish strength.
Moreover, in each of the above-described prior-art CMC shrouds, a-countermeasure against mismatch by a thermal expansion difference is not considered for any connected portion to the metal component. There is also a high possibility that a restricted portion is destroyed. Moreover, since a sealing property with the metal component is not considered, the cooling air leaks and deteriorates the capability. Furthermore, a shroud main body is directly exposed to a main-stream gas, and it is therefore difficult to use the shroud main body in high-temperature environment in which a main-stream gas temperature exceeds 1200° C. for a long time. Moreover, there has been a possibility that the whole shroud is destroyed at a collision time with a rotator blade tip end.